Process for the preparation of a composite ultraviolet absorber

Abstract

The application relates to the technical field of ultraviolet absorbing materials, and discloses a preparation method of a composite ultraviolet absorbing agent, which comprises the following components in percentage by weight: 50-70% of an ultraviolet absorbing agent, 10-20% of a light stabilizer, 5-15% of an antioxidant, 2-5% of a dynamic crosslinking agent, and 0.5-2% of an auxiliary additive. The preparation method comprises the following steps: dissolving the ultraviolet absorbing agent, the light stabilizer and the antioxidant in a mixed solvent to stir and form a uniform solution, adding the dynamic crosslinking agent to perform crosslinking reaction, then removing the solvent by vacuum evaporation, and grinding and drying to obtain the target product. The composite ultraviolet absorbing agent is prepared through the synergistic effect of the components and the construction of a dynamic crosslinking network, the ultraviolet absorbing performance, the chemical stability, the thermal stability and the low migration property are remarkably improved, and the composite ultraviolet absorbing agent can be widely applied in the fields of plastics, coatings, textiles and the like.

Description

Technical Field

[0001] This invention relates to the field of ultraviolet absorbing materials technology, specifically to a method for preparing a composite ultraviolet absorber. Background Technology

[0002] Ultraviolet (UV) absorbers, as an important class of functional chemical materials, are widely used in plastics, coatings, textiles, and other fields to prevent photodegradation, aging, and performance degradation of substrates caused by UV radiation. However, existing UV absorbers still have some significant drawbacks in practical applications, limiting their widespread adoption and long-term stable use.

[0003] First, traditional UV absorbers have limited absorption performance, especially in the wavelength range of 290–400 nm, where absorption efficiency is low. This allows some UV rays to penetrate the absorber layer and damage the substrate. Furthermore, these absorbers are prone to photochemical degradation under UV radiation, significantly reducing their lifespan and UV protection performance. Frequent addition or replacement of absorbers is necessary, increasing operating costs and complexity.

[0004] Secondly, existing absorbents often lack synergistic designs, making it difficult for a single component to simultaneously fulfill multiple functions such as UV absorption, antioxidant properties, and thermal stability. For example, some absorbents, even with good initial absorption performance, may fail due to rapid molecular degradation under UV-induced free radical and reactive oxygen species attack. Furthermore, the lack of effective synergistic protection from stabilizers or antioxidants often results in poor chemical stability and durability at high temperatures or during prolonged use.

[0005] Furthermore, absorbents also present migration issues during application. At high temperatures or in specific environments, absorbents can easily migrate or volatilize from the substrate, leading to a decrease in their protective performance and potentially adversely affecting the surface quality or mechanical properties of the substrate. Migration not only impacts the effectiveness of the absorbent but may also pose potential environmental and safety hazards.

[0006] Based on the shortcomings of the existing technology, there is an urgent need for a composite ultraviolet absorber that can effectively absorb ultraviolet light, has excellent chemical and thermal stability, and low migration. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing composite ultraviolet absorbers, which solves the problems of insufficient absorption performance, poor chemical and thermal stability, and high migration at high temperatures in existing ultraviolet absorbers.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a composite ultraviolet absorber that significantly improves ultraviolet absorption efficiency, chemical stability, and thermal stability through the synergistic effect of multiple components. The composite ultraviolet absorber comprises the following components by weight percentage:

[0010] UV absorber 50-70%;

[0011] Light stabilizer 10-20%;

[0012] Antioxidant 5-15%;

[0013] Dynamic crosslinking agent 2-5%;

[0014] Auxiliary additives: 0.5-2%.

[0015] The design of each component is described in detail below:

[0016] The ultraviolet absorber is the main functional component of this composite absorber. It is used to absorb ultraviolet light in the wavelength range of 290-400 nm and convert the ultraviolet light energy into harmless heat energy, thereby protecting the substrate from damage caused by ultraviolet radiation. This invention preferably uses triazine-benzotriazole compounds as ultraviolet absorbers. These compounds contain the following characteristics in their molecular structure: hydroxyl functional group: The hydroxyl group enhances the molecule's ability to absorb ultraviolet light through its strong electron-withdrawing effect and forms intramolecular hydrogen bonds to improve molecular stability.

[0017] Conjugated groups: Conjugated groups in a molecule can expand the conjugation range of the π-electron system, thereby reducing the excited state energy of the molecule and improving its stability under ultraviolet irradiation.

[0018] Upon absorbing ultraviolet light, triazine-benzotriazole compounds undergo an electron transition from the ground state to an excited state, releasing energy as heat or transferring it to the surrounding environment without radiation. The hydroxyl and conjugated groups in the molecular structure stabilize the excited-state energy during this process, preventing photochemical degradation. Furthermore, the thermal stability of the triazine structure allows it to maintain functional stability at high temperatures.

[0019] Light stabilizers

[0020] Light stabilizers are important synergistic components of composite ultraviolet absorbers. Their main function is to capture free radicals formed under ultraviolet irradiation, thereby protecting the molecular structure of the ultraviolet absorber. This invention preferably uses hindered amine light stabilizers. Hindered amine light stabilizers have the following functional characteristics:

[0021] Free radical scavenging ability: Hindered amine groups can efficiently capture active free radicals generated by ultraviolet light, thereby preventing free radicals from further attacking absorber molecules.

[0022] Self-repairing cycle mechanism: Hindered amine light stabilizers can cyclically act on free radical capture reactions by forming intermediates such as iminooxy radicals, thus making their photostable properties more durable.

[0023] During ultraviolet irradiation, hindered amine light stabilizers capture free radicals generated by light (such as hydroxyl radicals or peroxide radicals), preventing these free radicals from chemically reacting with absorber molecules or the substrate, thereby slowing down the degradation rate of the absorber. Simultaneously, their self-healing cycling mechanism ensures that the light stabilizer can capture free radicals multiple times, significantly extending the effective lifespan of the composite absorber.

[0024] antioxidants

[0025] The main function of antioxidants in composite absorbents is to neutralize reactive oxides (such as hydrogen peroxide and peroxide free radicals) induced by ultraviolet radiation, thereby further delaying the oxidative degradation of absorbent molecules. This invention preferably uses phenolic antioxidants or dithiophosphite compounds. Specific functions are as follows:

[0026] Phenolic antioxidants: They rapidly capture free radicals and terminate free radical chain reactions through the hydrogen-donating ability of their phenolic hydroxyl groups.

[0027] Dithiophosphites: The sulfur atoms in their molecules have high nucleophilicity, enabling them to react rapidly to form stable compounds, thereby preventing further oxidation.

[0028] Under photo-oxidative conditions, reactive oxygen species (ROS) readily attack the chemical bonds of absorbent molecules, leading to absorbent deactivation. Antioxidants can effectively capture these reactive species and convert them into stable intermediates, reducing damage to the absorbent. Simultaneously, after capturing reactive species, the products of antioxidant molecules still possess a certain degree of antioxidant capacity, thus achieving synergistic protection.

[0029] Dynamic crosslinking agent

[0030] Dynamic crosslinking agents connect ultraviolet absorbers, light stabilizers, and antioxidants into a stable molecular network through chemical bonds or physical forces, thereby enhancing intermolecular binding forces. This invention preferably uses triazine compounds, which have the following functional characteristics: Crosslinking: Triazine molecules undergo substitution reactions with hydroxyl or amino groups on absorber molecules through their active chlorine atoms, thereby forming a stable chemical crosslinked structure.

[0031] Dynamic network characteristics: The binding force between the crosslinking agent and other molecules can maintain a certain dynamic nature under high temperature conditions, so that the absorbent still has good flowability during processing.

[0032] Dynamic crosslinking agents, through the molecular network formed by chemical crosslinking, significantly enhance the overall stability of the composite absorbent. Under high-temperature conditions, the crosslinking network effectively prevents the migration or decomposition of absorbent molecules, thereby improving the thermal stability of the composite absorbent. Furthermore, due to the reversibility of the dynamic crosslinking network, the absorbent retains a certain degree of molecular mobility during processing, which helps to ensure its uniform dispersion with the substrate.

[0033] Additives

[0034] The auxiliary additives mainly include solvents and dispersants, used to improve the dispersibility of the absorbent and the operability of the preparation process. This invention preferably uses a mixed solvent of toluene and ethanol and a polyacrylate dispersant, the functions of which are as follows:

[0035] Mixed solvents: Toluene, as a non-polar solvent, can dissolve benzotriazole absorbents, while ethanol, as a polar solvent, can promote the dissolution of light stabilizers and antioxidants, thereby achieving uniform dispersion of multiple components.

[0036] Dispersants: Polyacrylate dispersants can form electrostatic repulsion between molecules, preventing the aggregation of composite absorbent particles.

[0037] The use of mixed solvents effectively reduces the solubility differences between different components, ensuring that the composite absorbent forms a uniformly distributed liquid phase system during the preparation process. Simultaneously, the dispersant significantly improves the dispersibility of the absorbent in the substrate through electrostatic or steric hindrance effects, preventing a decrease in absorption efficiency due to particle agglomeration.

[0038] Through the synergistic design of the above components, the composite ultraviolet absorber of the present invention exhibits significant improvements in ultraviolet absorption, photostability, and thermal stability. The ultraviolet absorber provides the core ultraviolet absorption function, while the photostability and antioxidants synergistically protect the absorber molecules through free radical capture and reactive oxygen species neutralization mechanisms. The dynamic crosslinking agent enhances structural stability through molecular networks, and the auxiliary additives optimize dispersibility and preparation process, thereby constructing a high-performance composite ultraviolet absorber.

[0039] Preferably, the ultraviolet absorber is a triazine-benzotriazole compound, whose molecular structure contains at least one hydroxyl group and one conjugated group. Specific compounds include, but are not limited to, the following compound: 2-(2'-hydroxy-5'-methylphenyl)-benzotriazole.

[0040] Its structural features are: a benzotriazole ring is connected to a hydroxyl-substituted phenyl group via a nitrogen atom, the hydroxyl group on the phenyl group is located in the ortho position of the benzotriazole ring, and the phenyl group also has a methyl substituent.

[0041] 2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)-benzotriazole

[0042] Its structural features are: a benzotriazole ring is connected to a phenyl group substituted with an ortho-hydroxyl group via a nitrogen atom, and the phenyl group contains two tert-butyl substituents at the para and symmetric positions of the hydroxyl group.

[0043] 2-(2'-hydroxy-3'-methoxyphenyl)-benzotriazole

[0044] Its structural features are: a benzotriazole ring is connected to a hydroxyl-substituted phenyl group via a nitrogen atom, the hydroxyl group on the phenyl group is located in the ortho position, and a methoxy substituent is located at the para position of the ortho hydroxyl group.

[0045] 2-(4'-hydroxy-3'-nitrophenyl)-benzotriazole

[0046] Its structural features are as follows: a benzotriazole ring is connected to a phenyl group containing a hydroxyl and a nitro substituent through a nitrogen atom, with the hydroxyl group on the phenyl group located at the para position and the nitro group located at the ortho position.

[0047] 2-(2'-hydroxy-4'-alkoxyphenyl)-benzotriazole

[0048] Its structural features are as follows: a benzotriazole ring is connected to a phenyl group containing hydroxyl and alkoxy substituents through a nitrogen atom, the hydroxyl group on the phenyl group is located at the ortho position, the alkoxy group is located at the para position, and the alkyl group can be methyl, ethyl or longer straight-chain alkyl.

[0049] All of the above compounds contain the core structure of benzotriazole, in which the nitrogen atom is covalently bonded to a benzene ring, and the benzene ring contains at least one hydroxyl group and one conjugated group (such as alkyl, nitro, alkoxy, or tert-butyl). These compounds are commercially available or synthesized by reacting benzotriazole with corresponding substituted aniline compounds.

[0050] Preferably, the light stabilizer is a hindered amine light stabilizer, whose chemical structure contains a piperidine ring, and which is modified by substituents to possess excellent free radical scavenging ability and photostability. Specific compounds include, but are not limited to, 2,2,6,6-tetramethylpiperidine alcohol.

[0051] Its structural features are: two methyl substituents at the 2 and 6 positions on the piperidine ring, and a hydroxyl functional group on the ring, with the hydroxyl group located at the 3 or 4 position.

[0052] 2,2,6,6-Tetramethylpiperidinemethanol

[0053] Its structural features are: a piperidine ring containing two methyl substituents at positions 2 and 6, respectively, and a hydroxymethyl group connected to another side chain (such as methyl or phenyl) on the piperidine ring.

[0054] N-(2,2,6,6-Tetramethylpiperidinyl)succinimide

[0055] Its structural features are: the piperidine ring has two methyl substituents at the 2 and 6 positions, the nitrogen atom on the piperidine ring is covalently linked to an imine structure, and the imine group further forms a stable compound with a dicarboxylic acid molecule (such as succinic anhydride).

[0056] N-(2,2,6,6-Tetramethylpiperidinyl)-2-acetylaniline

[0057] Its structural features are: the piperidine ring has two methyl substituents at the 2 and 6 positions, and the nitrogen atom of the piperidine ring is linked to the aniline ring through a linking group (such as an acetyl group).

[0058] Bis(2,2,6,6-tetramethylpiperidinyl)succinate

[0059] Its structural features are: two piperidine rings are connected by a diesterization reaction of succinic acid, and the piperidine rings have two methyl substituents at the 2 and 6 positions, forming a stable molecular network.

[0060] Tetramethylpiperidinylphenylformamide

[0061] Its structural features are: the piperidine ring has methyl substituents at the 2 and 6 positions, and the nitrogen atom of the piperidine ring is directly connected to the phenyl group through an amide group.

[0062] N-(2,2,6,6-Tetramethylpiperidinyl)malonic acid monoester

[0063] Its structural features are: the piperidine ring contains two methyl substituents at the 2 and 6 positions, which are connected to the monoester functional group through the malonic acid structure, and it has good dispersibility and stability.

[0064] The aforementioned hindered amine light stabilizer compounds exhibit significant free radical scavenging capabilities, and the steric hindrance effect of the methyl substituents on the piperidine ring effectively delays the occurrence of free radical chain reactions. They can be obtained through reactions of the piperidine ring with different acyl or carboxylic acid compounds, or directly through commercial routes.

[0065] Preferably, the antioxidant is a phenolic antioxidant or a dithiophosphite compound, whose chemical structure contains a phenolic hydroxyl group or a disulfide atom, and which has the ability to efficiently scavenge free radicals and inhibit oxidative chain reactions. Specific compounds include, but are not limited to, the following:

[0066] 1. Phenolic antioxidants

[0067] 2,6-Di-tert-butyl-4-methylphenol

[0068] Its structural features are as follows: the benzene ring has two large tert-butyl substituents at positions 2 and 6, and a methyl substituent at position 4. The phenolic hydroxyl group is located at position 1 of the benzene ring. The tert-butyl substituents protect the phenolic hydroxyl group from oxidation through steric hindrance, thus delaying the free radical chain reaction.

[0069] Butylated hydroxyanisole

[0070] Its structural features include a phenolic hydroxyl group at position 1 of the benzene ring, a tert-butyl group at position 4, and a methoxy group at position 2. The introduction of the methoxy group enhances the stability of the antioxidant and its free radical scavenging ability.

[0071] 4,4'-Methylenebis(2,6-di-tert-butylphenol)

[0072] Its structural features include two benzene rings connected by a methylene bridge, each benzene ring containing tert-butyl substituents at positions 2 and 6, and a phenolic hydroxyl group at position 1. The bisphenol structure further enhances its antioxidant capacity.

[0073] Tris(3,5-di-tert-butyl-4-hydroxyphenyl)propionate

[0074] Its structural feature is that three 3,5-di-tert-butyl-4-hydroxybenzene rings are linked by a propionate ester structure to form a molecule. Antioxidants with this structure have high molecular weight and good thermal stability.

[0075] 2. Dithiophosphite antioxidants

[0076] Di(alkyl)dithiophosphite

[0077] Its structural features include a dithiophosphite group (P(S)S) in the molecule, with two alkyl chains connected to the phosphorus atom via oxygen bonds. This antioxidant can capture peroxide free radicals and form stable products, thus inhibiting oxidation reactions.

[0078] Di(phenyl)dithiophosphite

[0079] Its structural feature is that the phosphorus atom in the dithiophosphite group is connected to two phenyl groups via oxygen bonds. The phenyl structure endows the molecule with higher thermal and oxidative stability.

[0080] Zinc di(isooctyl)dithiophosphite

[0081] Its structural features include: a dithiophosphite group forming a complex with zinc ions, and phosphorus atoms connecting two isooctyl chains via oxygen bonds. This compound not only possesses antioxidant capabilities but also synergistically improves the lubricity and stability of materials.

[0082] Di(isobutyl)dithiophosphite

[0083] Its structural features are: the phosphorus atom in the dithiophosphite group is connected to two isobutyl chains through oxygen bonds, which has strong antioxidant capacity and can remain stable at high temperatures.

[0084] Phenolic antioxidants utilize the phenolic hydroxyl group to capture free radicals through hydrogen donation, forming phenoxy radicals. These phenoxy radicals exhibit high stability due to the conjugation effect of the benzene ring, thus preventing the propagation of free radical chain reactions. Steric hindrance effects, such as those from the tert-butyl group, further protect the phenolic hydroxyl group from peroxidation.

[0085] Dithiophosphites react with reactive oxides (such as peroxide radicals) through their disulfide bonds, simultaneously forming stable sulfides and phosphate esters, thus blocking the oxidation reaction. These antioxidants are particularly suitable for high-temperature environments, maintaining their stability and function under extreme conditions.

[0086] The above compounds can be prepared by known chemical synthesis methods, such as by substitution reactions of phenolic compounds or by esterification reactions of dithiophosphorous acid with corresponding alcohols or phenolic compounds.

[0087] Preferably, the dynamic crosslinking agent is a triazine molecule whose chemical structure contains a 1,3,5-triazine ring with different substituents, enabling it to react chemically with functional groups (such as hydroxyl or amine groups) of other components to form a stable dynamic crosslinking network. Specific compounds include, but are not limited to, 2,4,6-trichloro-1,3,5-triazine.

[0088] Its structural features include chlorine atoms at positions 2, 4, and 6 of the 1,3,5-triazine ring. The chlorine atoms are highly reactive and can undergo substitution reactions with hydroxyl or amino groups in UV absorbers, light stabilizers, or antioxidants to form stable chemical bonds. This compound is widely used in cross-linking reactions, and its high reactivity allows the cross-linking process to be completed at relatively low temperatures.

[0089] 2-Amino-4,6-dichloro-1,3,5-triazine

[0090] Its structural features are: an amino group at position 2 of the triazine ring, and chlorine atoms at positions 4 and 6. The chlorine atom is used to react with the hydroxyl or amino group to form cross-linking bonds, while the amino group at position 2 can provide additional reactivity or form intermolecular interactions with other components through hydrogen bonds.

[0091] 2,4-Diamino-6-chloro-1,3,5-triazine

[0092] Its structural features include amino groups at positions 2 and 4 of the triazine ring, and a chlorine atom at position 6. The amino groups provide the compound with the ability to synergistically interact with multiple components, while the chlorine atom at position 6 forms a cross-linking bond through chemical reaction. Due to the introduction of the amino groups, this compound exhibits high water solubility and is suitable for aqueous cross-linking systems.

[0093] 2,4,6-Triamino-1,3,5-Triazine

[0094] Its structural features include amino substituents at positions 2, 4, and 6 of the triazine ring. Due to the lack of active chlorine, these compounds primarily form highly flexible cross-linked networks by forming hydrogen bonds or covalent bonds between the amino groups and other functional groups. This makes them particularly suitable for applications requiring high thermal stability.

[0095] 2-Ethoxy-4,6-dichloro-1,3,5-triazine

[0096] Its structural features are: an ethoxy group at the 2-position and chlorine atoms at the 4- and 6-positions of the triazine ring. The introduction of the ethoxy group enhances the stability of the molecule, while the chlorine atoms at the 4- and 6-positions still have high reactivity and can undergo cross-linking reactions with components such as absorbents and light stabilizers.

[0097] 2,4-Dihydroxy-6-chloro-1,3,5-triazine

[0098] Its structural features include hydroxyl groups at positions 2 and 4 of the triazine ring and a chlorine atom at position 6. The introduction of hydroxyl groups gives the compound high hydrophilicity, while the chlorine atom at position 6 forms crosslinks with other components through chemical bonds, improving the chemical stability of the composite material.

[0099] 2-Methyl-4,6-dichloro-1,3,5-triazine

[0100] Its structural features include a methyl group at position 2 and chlorine atoms at positions 4 and 6 of the triazine ring. The introduction of the methyl group enhances the hydrophobicity of the compound, making it suitable for cross-linking reactions in organic phase systems. The chlorine atoms at positions 4 and 6 can form stable cross-linking bonds with multiple components.

[0101] 2-Hydroxy-4,6-dichloro-1,3,5-triazine

[0102] Its structural features include a hydroxyl group at position 2 of the triazine ring and chlorine atoms at positions 4 and 6. The hydroxyl group can form weak intermolecular interactions with other molecules through hydrogen bonds, while the chlorine atoms at positions 4 and 6 can participate in chemical cross-linking.

[0103] The core of the triazine molecule lies in the substitution reactivity of its active chlorine atom or amino group:

[0104] Chlorine atom reaction: Active chlorine atoms can react with hydroxyl groups, amino groups, etc. in absorbent, light stabilizer or antioxidant molecules to generate stable amide bonds or ether bonds, thereby forming a cross-linked network.

[0105] The role of amino or hydroxyl groups: Some triazine compounds further enhance intermolecular stability through hydrogen bonds or covalent bonds, forming a dynamic cross-linked network.

[0106] The dynamic cross-linking effect of triazine molecules can significantly improve the chemical and thermal stability of composite absorbents, while avoiding molecular migration or decomposition during the use of traditional absorbents.

[0107] The above-mentioned triazine compounds can be prepared by known chemical methods, such as through amination, chlorination or alcoholysis to achieve chemical modification.

[0108] This invention also provides a method for preparing a composite ultraviolet absorber, specifically including the following steps:

[0109] Step S1: Ingredient Preparation

[0110] Accurately weigh the ultraviolet absorber, light stabilizer, antioxidant, dynamic crosslinking agent, and auxiliary additives according to the weight percentage range of each component of the composite ultraviolet absorber.

[0111] Ultraviolet absorbers: used to absorb ultraviolet light and protect materials.

[0112] Light stabilizers: capture free radicals and enhance the stability of ultraviolet absorbers.

[0113] Antioxidants: neutralize the active species generated by oxidation reactions and slow down material degradation.

[0114] Dynamic crosslinking agents: promote the formation of crosslinking networks between molecules, thereby enhancing chemical stability.

[0115] Auxiliary additives: used to improve dispersibility and processability.

[0116] Step S2: Solution mixing

[0117] The ultraviolet absorber, light stabilizer, and antioxidant are dissolved in a mixed solvent and stirred to form a homogeneous solution.

[0118] Preferred solvent: a mixed solution of toluene and ethanol (volume ratio 1:1).

[0119] Stirring conditions: Stir at room temperature (25-30℃) for 60-90 minutes until the solution is clear and uniformly dispersed.

[0120] The polarity difference of the mixed solvent can enhance the mutual solubility between multiple components and improve the homogeneity of the components.

[0121] Step S3: Dynamic cross-linking reaction

[0122] While stirring, a dynamic crosslinking agent is added dropwise to the homogeneous solution to initiate a crosslinking reaction.

[0123] Dynamic crosslinking agent addition rate: 0.5~1mL / min.

[0124] Stirring speed: 500-800 rpm.

[0125] Reaction temperature: 50~70℃.

[0126] Reaction time: 1 to 2 hours.

[0127] The active chlorine or amino groups in the dynamic crosslinking agent chemically bond with the hydroxyl or amine groups in the molecules of absorbent, light stabilizer and antioxidant to form a crosslinked structure.

[0128] Crosslinking reactions enhance the bonding force between multiple components through hydrogen bonds or covalent bonds, constructing a dynamic intermolecular network and improving the stability of composite materials.

[0129] Step S4: Solvent evaporation

[0130] The solution after the dynamic cross-linking reaction is completed is transferred to a vacuum evaporation device for solvent evaporation.

[0131] Evaporation temperature: 40~50℃.

[0132] Evaporation time: 3 to 5 hours.

[0133] Vacuum conditions: preferably maintain the pressure at 0.08 to 0.1 MPa.

[0134] Vacuum evaporation effectively removes solvents while avoiding component degradation caused by high temperatures. By controlling the evaporation rate, the stable formation of the cross-linked network structure is ensured.

[0135] Step S5: Grinding and Drying

[0136] The resulting solid composite was then ground and dried.

[0137] Target particle size for grinding: 5–20 μm.

[0138] Drying temperature: 40~60℃.

[0139] Drying time: 12-24 hours.

[0140] Drying conditions: Carry out under vacuum conditions to avoid oxidation or deliquescence.

[0141] By controlling particle size, the dispersion performance of the composite absorbent is improved, ensuring its uniform distribution within the substrate during application and achieving optimal UV absorption. The drying process guarantees the stability of the finished product and eliminates residual solvents.

[0142] Through the above steps, this invention provides a high-efficiency, stable, and industrially applicable composite ultraviolet absorber with a simple and easy preparation method and excellent product performance.

[0143] This invention provides a method for preparing a composite ultraviolet absorber. It has the following beneficial effects:

[0144] 1. This invention employs a triazine-benzotriazole ultraviolet absorber as its core component. This absorber's molecular structure contains hydroxyl and conjugated groups, enabling it to effectively absorb ultraviolet light in the wavelength range of 290–400 nm. Simultaneously, its high thermal and photostability ensures sustained high performance during long-term use. Optimization of the composite absorber's formulation and dispersibility significantly improves its ultraviolet absorption efficiency in various substrates.

[0145] 2. This invention introduces hindered amine light stabilizers and phenolic antioxidants to capture free radicals and reactive oxygen species (such as peroxides) during UV-induced photochemical and oxidative degradation, thereby protecting the molecular structure of the UV absorber from damage. The synergistic effect of the light stabilizers and antioxidants significantly slows down the degradation rate of the absorber and greatly improves the chemical stability of the composite absorber.

[0146] 3. This invention employs a triazine-based dynamic crosslinking agent to form a dynamic intermolecular crosslinking network between the absorbent, light stabilizer, and antioxidant, enhancing the bonding force and thermal stability among the multiple components. The dynamic crosslinking network exhibits excellent stability under high-temperature conditions, while effectively reducing the migration and decomposition of absorbent molecules in the substrate, making the composite absorbent more suitable for high-temperature processing scenarios.

[0147] 4. This invention achieves thorough dissolution and uniform dispersion of multiple components by using a mixed solvent of toluene and ethanol, and by precisely controlling the conditions of the dynamic crosslinking reaction (such as temperature, stirring rate, and reaction time). Through vacuum evaporation and particle size control, a solid composite absorbent with a particle size of 5–20 μm is finally obtained, ensuring its dispersibility and applicability in various substrates such as coatings, plastics, and textiles. Furthermore, the preparation process is simple, efficient, and suitable for industrial production. Detailed Implementation

[0148] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0149] Example 1:

[0150] Raw material ratio (by weight percentage):

[0151] UV absorber (2-(2'-hydroxy-5'-methylphenyl)-benzotriazole): 60%;

[0152] Light stabilizer (2,2,6,6-tetramethylpiperidinol): 15%;

[0153] Antioxidant (2,6-di-tert-butyl-4-methylphenol): 10%;

[0154] Dynamic crosslinking agent (2,4,6-trichloro-1,3,5-triazine): 3%;

[0155] Auxiliary additive (a mixture of toluene and ethanol, volume ratio 1:1): 12%.

[0156] Preparation method:

[0157] 1. Weigh out the ultraviolet absorber, light stabilizer, antioxidant and dynamic crosslinking agent according to the above proportions and set aside.

[0158] 2. Add the UV absorber, light stabilizer, and antioxidant to the mixed solvent of toluene and ethanol, stir to form a homogeneous solution, stir for 80 minutes at a temperature of 25°C.

[0159] 3. Add the dynamic crosslinking agent dropwise to the solution (addition rate of 0.8 mL / min) while stirring (600 rpm) and react at 60 °C for 1.5 hours.

[0160] 4. Transfer the reaction solution to a vacuum evaporation apparatus and evaporate the solvent at 45°C for 3.5 hours to obtain a solid composite.

[0161] 5. The solid composite was ground to achieve a particle size of 10 μm, and then dried in a vacuum drying oven at 50 °C for 16 hours to obtain a composite ultraviolet absorber.

[0162] Example 2:

[0163] Raw material ratio (by weight percentage):

[0164] UV absorber (2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)-benzotriazole): 65%;

[0165] Light stabilizer (N-(2,2,6,6-tetramethylpiperidinyl)succinimide): 12%;

[0166] Antioxidant (tris(3,5-di-tert-butyl-4-hydroxyphenyl)propionate): 8%;

[0167] Dynamic crosslinking agent (2-amino-4,6-dichloro-1,3,5-triazine): 3%;

[0168] Auxiliary additive (a mixture of toluene and ethanol, volume ratio 1:1): 12%.

[0169] Preparation method:

[0170] 1. Weigh the raw materials according to the proportions and set aside.

[0171] 2. Dissolve the UV absorber, light stabilizer, and antioxidant in a mixed solvent of toluene and ethanol, and stir at 25°C for 90 minutes until homogeneous.

[0172] 3. While stirring (700 rpm), add the dynamic crosslinking agent dropwise at a rate of 0.7 mL / min. The reaction temperature is 55 °C and the reaction time is 1 hour.

[0173] 4. After the reaction, the solvent is transferred to a vacuum evaporation apparatus and evaporated at 50°C for 4 hours.

[0174] 5. The obtained solid composite was ground to a particle size of 8 μm, and then dried in a vacuum drying oven at 45 °C for 20 hours to obtain the target composite ultraviolet absorber.

[0175] Example 3:

[0176] Raw material ratio (by weight percentage):

[0177] UV absorber (2-(2'-hydroxy-3'-methoxyphenyl)-benzotriazole): 55%;

[0178] Light stabilizer (2,2,6,6-tetramethylpiperidinemethanol): 18%;

[0179] Antioxidant (butylated hydroxyanisole): 10%;

[0180] Dynamic crosslinking agent (2,4-dihydroxy-6-chloro-1,3,5-triazine): 4%;

[0181] Auxiliary additive (a mixture of toluene and ethanol, volume ratio 1:1): 13%.

[0182] Preparation method:

[0183] 1. Weigh each raw material according to the above proportions.

[0184] 2. Dissolve the UV absorber, light stabilizer and antioxidant in a mixed solvent, stir until uniformly dissolved, at 30°C for 60 minutes.

[0185] 3. The dynamic crosslinking agent was added dropwise to the solution at a rate of 0.5 mL / min, the reaction temperature was 50℃, the stirring speed was 500 rpm, and the reaction time was 2 hours.

[0186] 4. Transfer the reaction solution into a vacuum evaporator, evaporate at 40°C for 3 hours to obtain a solid composite.

[0187] 5. After grinding the solid composite to a particle size of 15 μm, dry it in a vacuum drying oven at 50°C for 12 hours to obtain the finished product.

[0188] Example 4:

[0189] Raw material ratio (by weight percentage):

[0190] UV absorber (2-(4'-hydroxy-3'-nitrophenyl)-benzotriazole): 60%;

[0191] Light stabilizer (bis(2,2,6,6-tetramethylpiperidinyl)succinate): 12%;

[0192] Antioxidant (2,6-di-tert-butyl-4-methylphenol): 10%;

[0193] Dynamic crosslinking agent (2,4,6-triamino-1,3,5-triazine): 3%;

[0194] Auxiliary additive (a mixture of toluene and ethanol, volume ratio 1:1): 15%.

[0195] Preparation method:

[0196] 1. Add the UV absorber, light stabilizer and antioxidant to the mixed solvent and stir at room temperature until dissolved and homogeneous for 75 minutes.

[0197] 2. Add the dynamic crosslinking agent dropwise at a rate of 0.6 mL / min, at a reaction temperature of 65℃, a stirring speed of 700 rpm, and a reaction time of 1.5 hours.

[0198] 3. The solvent was removed by vacuum evaporation at 45°C for 4 hours to obtain a solid composite.

[0199] 4. After grinding the solid composite to a particle size of 10 μm, it was vacuum dried at 40 °C for 16 hours to obtain the target product.

[0200] Example 5:

[0201] Raw material ratio (by weight percentage):

[0202] UV absorber (2-(2'-hydroxy-4'-alkoxyphenyl)-benzotriazole, alkoxy group is ethoxy): 62%;

[0203] Light stabilizer (N-(2,2,6,6-tetramethylpiperidinyl)-2-acetylaniline): 15%;

[0204] Antioxidant (di(phenyl)dithiophosphite): 8%;

[0205] Dynamic crosslinking agent (2-ethoxy-4,6-dichloro-1,3,5-triazine): 3%;

[0206] Auxiliary additive (a mixture of toluene and ethanol, volume ratio 1:1): 12%.

[0207] Preparation method:

[0208] 1. Weigh each ingredient according to the proportion, add them to the mixed solvent, and stir at room temperature for 70 minutes.

[0209] 2. Add the dynamic crosslinking agent dropwise (at a rate of 0.8 mL / min), stir at 600 rpm, react at 60°C for 2 hours.

[0210] 3. Transfer the reaction solution to a vacuum evaporator and evaporate at 45°C for 4 hours.

[0211] 4. After grinding the obtained solid material to a particle size of 5 μm, dry it in a vacuum drying oven at 60°C for 12 hours to obtain the target product.

[0212] Example 6:

[0213] Raw material ratio (by weight percentage):

[0214] UV absorber (2-(2'-hydroxy-5'-methylphenyl)-benzotriazole): 58%;

[0215] Light stabilizer (2,2,6,6-tetramethylpiperidinol): 14%;

[0216] Antioxidant (tris(3,5-di-tert-butyl-4-hydroxyphenyl)propionate): 12%;

[0217] Dynamic crosslinking agent (2,4-diamino-6-chloro-1,3,5-triazine): 4%;

[0218] Auxiliary additive (a mixture of toluene and ethanol, volume ratio 1:1): 12%.

[0219] Preparation method:

[0220] 1. Weigh out the ultraviolet absorber, light stabilizer and antioxidant, add them to the mixed solvent and stir for 90 minutes at 30°C.

[0221] 2. Add the dynamic crosslinking agent dropwise to the solution at a rate of 0.9 mL / min, at a reaction temperature of 65℃, a stirring speed of 800 rpm, and a reaction time of 1 hour.

[0222] 3. Evaporate the solvent under vacuum (40°C) for 3 hours to obtain a solid composite.

[0223] 4. After grinding the solid material to a particle size of 20μm, dry it in a vacuum drying oven at 50℃ for 24 hours to obtain a composite ultraviolet absorber.

[0224] Comparative Example 1:

[0225] Based on Example 1, the difference is that the content of the light stabilizer (2,2,6,6-tetramethylpiperidinol) is reduced from 15% to 5%, while the remaining components and preparation process remain unchanged.

[0226] Comparative Example 2:

[0227] Based on Example 3, the difference is that the dynamic crosslinking agent (2,4-dihydroxy-6-chloro-1,3,5-triazine) is completely removed from the formulation, while other components and processes remain unchanged.

[0228] Comparative Example 3:

[0229] Based on Example 2, the difference is that the antioxidant (tris(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) was completely removed from the formulation, while the other components and processes remained unchanged.

[0230] Comparative Example 4:

[0231] Based on Example 5, the difference is that the ultraviolet absorber (2-(2'-hydroxy-4'-alkoxyphenyl)-benzotriazole) is replaced with a conventional benzophenone-based ultraviolet absorber, while other components and processes remain unchanged.

[0232] Comparative Example 5:

[0233] Based on Example 6, the difference is that the mixed solvent (a mixture of toluene and ethanol in a volume ratio of 1:1) is changed to pure toluene, while other components and processes remain unchanged.

[0234] Comparative Example 6:

[0235] Based on Example 4, the difference is that the temperature of the dynamic crosslinking reaction is increased from 60°C to 90°C, while other components and processes remain unchanged.

[0236] Comparative Example 7:

[0237] Based on Example 1, the difference is that the grinding particle size is increased from 10 μm to 50 μm, while other components and processes remain unchanged.

[0238] Test Example 1:

[0239] Experimental materials and equipment: Samples from Examples 1-6; samples from Comparative Examples 1, 4, and 7; polypropylene substrate (additive carrier).

[0240] Equipment: Ultraviolet-Vis spectrophotometer (UV-Vis); grinding equipment; homogenizer.

[0241] Experimental steps

[0242] 1. Sample preparation:

[0243] All samples were prepared according to the formulations of the examples and comparative examples (the particle size was controlled in the range of 5 to 20 μm, except for comparative example 7).

[0244] The sample was mixed with a polypropylene substrate at 2% (by mass) and stirred evenly using a homogenizer to prepare a homogeneous polypropylene additive mixture.

[0245] 2. Test sample production:

[0246] The mixture was prepared into uniform thin sheets (200 μm thick) by hot pressing to ensure that the sheets were flat and free of air bubbles.

[0247] Cut a test sample with a size of 20mm×20mm.

[0248] 3. Test conditions:

[0249] A UV-Vis spectrophotometer was used, with a scanning wavelength range of 290–400 nm and an interval of 2 nm.

[0250] Set air as the blank control.

[0251] Each sample was tested three times, and the average absorbance data was recorded.

[0252] 4. Data Processing:

[0253] Based on the absorbance data, the absorption efficiency of the sample for ultraviolet light in the wavelength range of 290–400 nm was calculated.

[0254] Absorption efficiency calculation formula:

[0255]

[0256] Among them, A 样品 A represents the absorbance of the sample at a specific wavelength. 对照 This is the standard reference absorbance.

[0257] The test results are shown in Table 1:

[0258] Table 1 Comparison of UV absorption efficiency and absorbance

[0259] Sample number Average absorbance (wavelength range 290–400 nm) Absorption efficiency (%) Example 1 2.87 98.5 Example 2 2.85 97.9 Example 3 2.78 95.8 Example 4 2.81 96.8 Example 5 2.9 99.3 Example 6 2.83 97.4 Comparative Example 1 1.98 66.5 Comparative Example 4 2.12 72.4 Comparative Example 7 2.45 83.6

[0260] The results of Test Example 1 demonstrate that the composite ultraviolet absorber of this invention significantly outperforms the comparative sample in ultraviolet absorption performance, thanks to optimized component design and process control. The triazine-benzotriazole absorber used in the examples possesses hydroxyl and conjugated groups in its molecular structure that effectively absorb ultraviolet light within the wavelength range. Simultaneously, through intramolecular conjugation and hydrogen bonding stabilization mechanisms, it avoids photochemical degradation under high-intensity ultraviolet irradiation. In contrast, the conventional benzophenone absorber used in Comparative Example 4 lacks these structural features, resulting in a significant reduction in absorbance and absorption efficiency, thus proving the advantages of the triazine-benzotriazole absorber in terms of absorption performance and chemical stability.

[0261] Furthermore, the synergistic effect of the light stabilizer and dynamic crosslinking agent in this invention significantly improves the overall performance of the absorbent. The hindered amine light stabilizer used in the examples effectively delays UV-induced degradation of absorbent molecules through a free radical capture mechanism, while the dynamic crosslinking agent further stabilizes the system structure by constructing a dynamic intermolecular network, ensuring uniform dispersion and thermal stability of the absorbent. In Comparative Example 1, insufficient light stabilizer content led to the accumulation of free radicals that damaged the absorbent molecules, while in Comparative Example 7, the dispersibility and absorption efficiency of the system significantly decreased due to excessively large particle size. These results fully verify the criticality of light stabilizer content and particle size control for performance optimization, and highlight the technical advantages and innovations of this invention from the perspective of molecular synergy and dispersibility.

[0262] Test Example 2:

[0263] Experimental materials and equipment: Samples from Examples 1-3; samples from Comparative Examples 2, 3, and 4; polypropylene film (coated substrate).

[0264] Equipment: Ultraviolet accelerated aging test chamber (wavelength 340nm, power 0.76W / m) 2 ); UV-Vis spectrophotometer; precision coating equipment (coating thickness control).

[0265] Experimental steps

[0266] 1. Sample preparation:

[0267] Samples were prepared according to the formulations of Examples 1-3 and Comparative Examples 2, 3, and 4, with the particle size controlled at 10 μm.

[0268] Each sample was uniformly coated on the surface of a polypropylene film at 2% (by mass), with a coating thickness of 20 μm.

[0269] 2. Ultraviolet aging test:

[0270] The coated sample film was placed in an accelerated UV aging test chamber.

[0271] Aging conditions: wavelength 340nm, power 0.76W / m 2 Temperature 50℃, humidity controlled at 50% RH.

[0272] The aging time was set to 500 hours, and samples were taken every 100 hours to test absorbance and residual rate.

[0273] 3. Performance Testing:

[0274] Take out the samples after each stage of aging and measure the absorbance using a UV-Vis spectrophotometer (wavelength range 290–400 nm, 2 nm interval).

[0275] Calculate the residual rate:

[0276]

[0277] Each sample was tested three times, and the average value was recorded.

[0278] The test results are shown in Table 2:

[0279] Table 2 Comparison of Residual Rates in UV Aging Tests

[0280]

[0281] The results of Test Example 2 further validated the significant stability of the composite UV absorber of the present invention under UV irradiation conditions, mainly due to the optimized component design and synergistic effect. The triazine-benzotriazole absorber in the examples, through the combination of hydroxyl groups and conjugated groups, not only exhibited excellent UV absorption capacity but also avoided photo-induced degradation reactions through an intramolecular energy dispersion mechanism. Simultaneously, the hindered amine photostable agent, by capturing free radicals, prevented the damage of absorber molecules to reactive free radicals generated by UV irradiation; the antioxidant further protected the chemical stability of the entire system by neutralizing peroxides and other oxides. In contrast, Comparative Example 3, due to the lack of antioxidants, failed to effectively scavenge reactive oxygen free radicals, resulting in a significantly increased degradation rate of the absorber. Comparative Example 4, using a traditional benzophenone absorber, lacked stabilizing properties in its molecular structure, leading to significant photo-induced degradation.

[0282] Furthermore, the addition of a dynamic crosslinking agent in this invention significantly enhances the structural stability of the absorbent. Through chemical bonding with the absorbent and stabilizer, the dynamic crosslinking agent forms a stable intermolecular crosslinking network, effectively inhibiting the migration and decomposition of absorbent molecules under UV irradiation. Experimental results show that, in Comparative Example 2, the residual performance of the absorbent rapidly declines in the absence of the dynamic crosslinking agent, exhibiting poor chemical stability. The formation of the dynamic crosslinking network in the examples also improves the overall system's dispersion and uniformity, thereby ensuring the stable performance of the absorbent in aging tests. These results fully demonstrate the crucial role of absorbent molecular design and the synergistic effect of auxiliary components in improving the performance of UV absorbers, and further verify the innovation and superiority of the technical solution of this invention.

[0283] Test Example 3:

[0284] Experimental materials and equipment: Samples from Examples 2, 5, and 6; samples from Comparative Examples 2, 6, and 7; polyethylene film (substrate).

[0285] Equipment: Thermogravimetric analyzer (TGA); vacuum oven; precision electronic balance; n-hexane (for testing of migratory solvents).

[0286] Experimental methods

[0287] (A) Thermal stability test

[0288] 1. Sample preparation:

[0289] Samples were prepared according to the formulations of the examples and comparative examples, with the particle size controlled at 10 μm, and dried to constant weight.

[0290] 2. Test conditions:

[0291] A 5 mg sample was placed in a platinum crucible and tested in a thermogravimetric analyzer.

[0292] The heating rate is 10℃ / min, and the temperature range is from room temperature to 400℃.

[0293] The test was conducted under nitrogen protection, and the mass of the sample was recorded as a function of temperature.

[0294] 3. Data Recording:

[0295] Record the decomposition temperature (T) of the sample. d (The temperature at which sample mass loss reaches 5%).

[0296] Record the percentage of the residual mass of the sample at 400℃ (residual mass).

[0297] (B) Transfer testing

[0298] 1. Sample preparation:

[0299] The sample was uniformly coated on the surface of a polyethylene film at a mass ratio of 2%, with a coating thickness of 20 μm.

[0300] The coated film was placed in a vacuum drying oven and baked at 100°C for 72 hours.

[0301] 2. Solvent soaking:

[0302] Remove the film and soak the surface in n-hexane (soaking time is 2 hours).

[0303] The hexane solution was recovered by rotary evaporation and dried to constant weight. The mass of the migrating material was recorded.

[0304] 3. Mobility calculation:

[0305] Mobility calculation formula:

[0306]

[0307] The test results are shown in Table 3:

[0308] Table 3. Results of Thermal Stability and Migration Tests

[0309] Sample number <![CDATA[Decomposition temperature (T d , °C)]]> Residual mass (%) Migration rate (%) Example 2 315 19.2 1.5 Example 5 320 20.3 1.2 Example 6 310 18.5 1.7 Comparative Example 2 250 5.8 6.8 Comparative Example 6 280 10.4 4.5 Comparative Example 7 290 14.2 3.8

[0310] The results of Test Example 3 demonstrate that the composite UV absorber of this invention exhibits excellent thermal stability and low migration under high-temperature conditions, primarily due to the synergistic effect between components and the construction of a dynamic cross-linking network. In this example, the dynamic cross-linking agent forms an intermolecular dynamic cross-linking network through chemical bonding with the absorber, photostabilizer, and antioxidant, effectively inhibiting the decomposition and migration of absorber molecules under high-temperature conditions. This cross-linking network not only enhances the thermal stability of the material but also provides a uniform molecular distribution environment, allowing the system to maintain good structural integrity even at high temperatures. In contrast, Comparative Example 2 lacks a dynamic cross-linking agent, leading to rapid decomposition of absorber molecules at high temperatures, manifested as a significant decrease in decomposition temperature and a rapid reduction in residual mass, verifying the core role of the cross-linking agent in improving thermal stability.

[0311] Meanwhile, the low migration observed in the examples also demonstrates the immobilization effect of the dynamic crosslinking agent on absorbent molecules under high-temperature conditions. The dynamic crosslinking network effectively reduces the risk of absorbent release from the substrate by restricting the degrees of freedom of the molecular chains. Furthermore, particle size optimization further improves the dispersibility of the absorbent and reduces the destructive impact of locally overly concentrated areas on system stability. Comparative Example 7, due to its excessively large particle size and poor dispersibility, exhibited a significantly increased migration rate. Comparative Example 6, due to its excessively high dynamic crosslinking reaction temperature, experienced degradation of some components, resulting in an incomplete crosslinking network and also exhibiting high migration. These results fully demonstrate the stabilizing effect of the dynamic crosslinking network and the importance of process optimization for absorbent performance, further highlighting the innovation and superiority of this invention in solving the problems of absorbent thermal stability and migration.

[0312] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A composite ultraviolet absorber, characterized in that, The composite ultraviolet absorber is a solid composite obtained by chemical reaction of the following components in weight percentage: UV absorber 50-70%; Light stabilizer 10-20%; Antioxidant 5-15%; Dynamic crosslinking agent 2-5%; Auxiliary additives: 0.5-2%; The ultraviolet absorber is a triazine-benzotriazole compound, whose molecular structure contains at least one hydroxyl group and one conjugated group; The dynamic crosslinking agent is a triazine molecule selected from 2,4,6-trichloro-1,3,5-triazine and its derivatives.

2. The composite ultraviolet absorber according to claim 1, characterized in that, The light stabilizer is a hindered amine light stabilizer, selected from 2,2,6,6-tetramethylpiperidinol and its derivatives.

3. The composite ultraviolet absorber according to claim 1, characterized in that, The antioxidant is a phenolic antioxidant, selected from 2,6-di-tert-butyl-4-methylphenol or dithiophosphite compounds.

4. A method for preparing a composite ultraviolet absorber, characterized in that, Includes the following steps: S1. Weigh out the ultraviolet absorber, light stabilizer, antioxidant, dynamic crosslinking agent and auxiliary additives according to the weight percentage range of each component of the composite ultraviolet absorber according to any one of claims 1-3. S2. Dissolve the ultraviolet absorber, light stabilizer and antioxidant in a mixed solvent and stir to form a homogeneous solution; S3. Add the dynamic crosslinking agent dropwise to the homogeneous solution and stir the reaction at 50-70°C. S4. Vacuum evaporate the solution after the reaction to remove the solvent and obtain a solid complex. S5. Grind and dry the obtained solid composite to obtain a composite ultraviolet absorber.

5. The method for preparing the composite ultraviolet absorber according to claim 4, characterized in that, The mixed solvent is a mixture of toluene and ethanol, with a volume ratio of toluene to ethanol of 1:

1.

6. The method for preparing the composite ultraviolet absorber according to claim 4, characterized in that, In the dynamic crosslinking reaction, the addition rate of the dynamic crosslinking agent is 0.5–1 mL / min, the stirring rate is 500–800 rpm, and the reaction time is 1–2 hours.

7. The method for preparing the composite ultraviolet absorber according to claim 4, characterized in that, The solvent evaporation is carried out at 40–50°C for 3–5 hours.

8. The method for preparing the composite ultraviolet absorber according to claim 4, characterized in that, The particle size of the ground solid composite is 5–20 μm.

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